Suspected pirates have kidnapped six crew members from a German-owned container ship off the coast of southern Nigeria, maritime site SeaGuardian reports.

It says that the ship was en route from Equatorial Guinea's port city of Malabo to Liberia's capital, Monrovia.

The report says that at least eight pirates boarded the ship and kidnapped the crew, including the captain.

it adds that the remaining 12 crew were unhurt and resumed sailing to Monrovia where the ship is expected to dock on Wednesday.

The AFP news agency reports that the Liberia-flagged vessel is owned by Germany's Peter Doehle Group.

The shipping firm said it would not disclose the nationalities of those abducted "for security reasons", it says.

The International Maritime Bureau (IMB) has recorded 121 piracy incidents in international waters this year, including shootings, attempted kidnappings and hijackings of ships.

It described in a report published last week that the Gulf of Guinea remained a "hot spot for attacks", despite a fall in the number of incidents elsewhere in the world, AFP reports.